A vehicle may use one or more dynamoelectric machines as a source of motive power. Such dynamoelectric machines may serve as a prime mover powered by an off-board electric power source, such as by way of a catenary wire or “third rail”, or with an on-board electric power source, such as an electric battery. Alternatively, they may serve as part of a power train for some other type of prime mover, such as an internal combustion engine, wherein the engine may drive one dynamoelectric machine as an electric generator and one or more additional dynamoelectric machines serve as electric motors powered by the generator that drive one or more wheels for the vehicle. A dynamoelectric machine may also serve both motor and generator functions, wherein such a machine may accelerate and de-accelerate the vehicle.
When a vehicle has a prime mover of the dynamoelectric machine type wherein power transfer from the prime mover must be sufficient to control the movement of the entire vehicle, the dynamoelectric machine must have sufficient torque and power to control the vehicle under worst-case conditions. In some cases the size and weight of such a machine exceeds design requirements for the vehicle. Furthermore, a fault that occurs in such a machine results in total failure of the vehicle.